A 74-year-old woman had been on hemodialysis for about 2 months using a short-term indwelling dialysis catheter due to chronic kidney disease. A 20 mm-diameter left atrial neoplastic lesion was noted during a screening echocardiogram performed at the time of induction of hemodialysis. The lesion rapidly increased to 30 mm 2 months later and was referred to our hospital for surgical resection. Under cardiopulmonary bypass and cardiac arrest, tumor resection was performed. Although the lesion was myxomatous with a thin stalk on the left atrial ceiling, the pathological diagnosis was thrombus. After the initiation of anticoagulation, the patient was discharged.